I believe you accidentally posted this in the wrong forum. Maybe you didn't notice the "JD" in the title "JD Owning/Operating".
There may be an adjustment in the linkage from the pedal to the transmission that will allow you get a higher speed when the pedal is at its limit. Depending on the setup, if you adjust for a higher maximum reverse speed, you may get a lower maximum forward speed.
Consider posting this under "NH Owning/Operating" so someone familiar with your tractor can give you a more definite answer.